/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.transforms;



import com.bff.gaia.unified.sdk.values.KV;

import com.bff.gaia.unified.sdk.values.PCollection;

import com.bff.gaia.unified.sdk.transforms.windowing.WindowFn;



/**

 * {@code Values<V>} takes a {@code PCollection} of {@code KV<K, V>}s and returns a {@code

 * PCollection<V>} of the values.

 *

 * <p>Example of use:

 *

 * <pre>{@code

 * PCollection<KV<String, Long>> wordCounts = ...;

 * PCollection<Long> counts = wordCounts.apply(Values.<Long>create());

 * }</pre>

 *

 * <p>Each output element has the same timestamp and is in the same windows as its corresponding

 * input element, and the output {@code PCollection} has the same {@link

 * WindowFn} associated with it as the input.

 *

 * <p>See also {@link Keys}.

 *

 * @param <V> the type of the values in the input {@code PCollection}, and the type of the elements

 *     in the output {@code PCollection}

 */

public class Values<V> extends PTransform<PCollection<? extends KV<?, V>>, PCollection<V>> {

  /**

   * Returns a {@code Values<V>} {@code PTransform}.

   *

   * @param <V> the type of the values in the input {@code PCollection}, and the type of the

   *     elements in the output {@code PCollection}

   */

  public static <V> Values<V> create() {

    return new Values<>();

  }



  private Values() {}



  @Override

  public PCollection<V> expand(PCollection<? extends KV<?, V>> in) {

    return in.apply(

        "Values",

        MapElements.via(

            new SimpleFunction<KV<?, V>, V>() {

              @Override

              public V apply(KV<?, V> kv) {

                return kv.getValue();

              }

            }));

  }

}